Topical anaesthesia in ophthalmology. Local infiltration for Caesarean section. Trigeminal nerve block, страница 2

3. Incise the rectus sheath (Fig. 49:1) and gently retract the rectus muscle to expose the posterior rectus sheath, which ends at the arcuate line midway between the umbilicus and the pubis.

4. Infiltrate below the posterior rectus sheath above the arcuate line and directly into the extraperitoneal tissue (transversalis fascia) below the line(10-15 ml). (Fig. 49:2).

5. Open the peritoneal cavity and expose the uterus.

6. Expose the utero-vesical fold of peritoneum and infiltrate it (10-15 ml) (Fig. 49:3). The peritoneum may now be incised and the lower uterine segment exposed by gently pushing away the bladder (Fig. 49:4).

7. Infiltrate the uterine wall along the proposed incision (10-15 ml).

8. Incise the wall and extract the foetus.

9. Complete the operation

Drugs and dose

LidocaineO.5% 60-100 ml, 0.5% mepivacaine, 0.125% bupivacaine. Epinephrine 1:200.000 may be added.

Intravenous regional anaesthesia (Bier's block)

Intravenous regional anaesthesia is a simple and effective method of producing anaesthesia of the limbs, both upper and lower. It is based on the fact that If the circulation to a limb is occluded and an injection of local anaesthetic is made into a vein distal to that occlusion, the drug will reach the capillaries by retrograde flow and enter the extravascular space. Here it will come into contact with nerve endings and nerve trunks, causing numbness and paralysis of the limb below the tourniquet for the duration of the circulatory occlusion.

Method

Upper limb

1. All drugs, oxygen and equipment necessary for the treatment of toxicity should be available. Venous access in the non-operated limb should be established.

2. An inflatable tourniquet is placed around the upper arm over a wool bandage to protect the skin. Ideally, the tourniquet should be one specially designed for the purpose with a gauge and hand pump (Fig. 51:1).

Alternatively, an ordinary sphygmomanom-eter cuff may be used if essential precautions are taken. It must be very carefully tested for leaks and the connection to the mercury column or pressure gauge must be totally secure. Once the cuff is pressurised, it is vital that deflation below arterial pressure does not occur accidentally. To prevent sudden deflation due to slipping of the cuff, a non-elastic bandage should be wrapped around the cuff (Fig. 51:2).

3. A needle, a 23 gauge butterfly needle (Fig. 51:3) or a small IV plastic cannula, is placed into a vein on the dorsum of the hand and secured to the skin.

4. The limb is exsanguinated of venous blood. This may be done by applying an Esmarch or elastic bandage from the hand up to the blood pressure cuff (Fig. 51:4). In cases of fractures when this process may be painful, the limb may simply be raised vertical for a few minutes to empty the veins as much as possible, without applying the bandage (Fig. 51:5).

5. The blood pressure cuff is then inflated to 250 mmHg or 100 mmHg above systolic pressure, and the Esmarch or elastic bandage below the cuff removed (Fig. 51:6)

6. Local anaesthetic is now injected into the indwelling needle. This injection should be slow, not exceeding 1 ml every 2 s. The drug will be seen to enter the capillaries and produce pale areas of skin (Fig. 51:7).

7. At least 10-15 min must be allowed to achieve anaesthesia before beginning the surgical procedure (Fig. 51:8).

8. Following the completion of surgery, and not within 20 min of completing the local anaesthetic injection, the blood pressure cuff may be deflated. The longer the tourniquet is in place, the more local anaesthetic will reach the extracellular space, reducing the amount of drug which will be released on removal of the tourniquet.

9. Normal sensation and muscle function will return within a few minutes, though patchy anaesthesia may remain for up to 60 min.

Drugs and dose

40 ml is usually required in an adult though this should be reduced in children (0.5 ml/kg body weight) or if the limb is clearly small and thin. The solution must be dilute, i.e. 0.5% of prilocaine, lidocaine or mepivacaine. Other agents such as bupivacaine are not recommended nor should epinephrine be added. Remember the drug is being injected intravenously and toxicity can easily occur with accidental deflation of the cuff. Too rapid an injection can produce a high pressure within the veins and drug can escape past the tourniquet. This may also occur if the veins are not emptied before the injection.